Field of the Invention
This invention relates generally to a method for assembling structures and, in one particular embodiment, to a method for providing a beam on a vehicle, where the method includes providing a back plate of the beam made of metal that is attached to a vehicle frame structure, subjecting the frame structure to high temperature processes, and then attaching a front assembly of the beam to the back plate after the high temperature processes are complete, where the back plate is designed to provide structural integrity that allows the vehicle frame structure to go through the high temperature processes and/or the vehicle frame structure provides structural integrity that allows the back plate to go through the one or more processes, and where the back plate is also designed to provide desired functional characteristics of the beam.
Discussion of the Related Art
Modern vehicles are equipped with a number of impact beams that provide structural integrity against collisions and impacts with objects, such as other vehicles. More particularly, impact beams are traditionally used in vehicle designs to protect occupants from front, side and/or rear impacts by absorbing energy through deformation in the event of a vehicle crash and distributing the applied dynamic loads to other energy absorbing sub-systems on the vehicle. For example, it is known to provide impact beams in a front energy management or bumper assembly, a rear energy management or bumper assembly and side impact assemblies on a vehicle. Impact beams at the front and rear of the vehicle are usually referred to as bumper beams, and impact beams on the sides of the vehicle are sometimes referred to as anti-intrusion bars.
In all cases, it is desirable to provide an impact beam with low mass, high flexural stiffness and strength, and high energy absorption per unit mass. The lightweight requirement is predicated by fuel economy standards and the fact that impact beams are located both very close to and very far from the vehicle's center of mass. Maximizing the flexural stiffness and strength is necessary if the beam is to survive low speed impacts without damage and transfer impact loads throughout the duration of a high speed impact event. Further, a high level of energy absorption translates into reduced load transfer to the occupants of the vehicle, thus increasing safety.
In one known vehicle front energy management system, an impact beam is comprised of a top and bottom facesheet in combination with an internal structural core for providing high energy impact resistance in a light weight and cost effective manner. Typically, the impact beam for such a system includes aluminum, steel, carbon fiber, etc. layers that are extruded, roll-formed, etc. A hard energy absorbing layer may be formed on the impact beam having the general shape of an outer fascia trim panel on the side closer to the fascia and that of the front face of the impact beam on the side closer to the impact beam. A soft energy absorbing layer is then formed on the hard energy absorbing layer and the front fascia panel is then provided over the soft energy absorbing layer. The combination of the hard energy absorbing layer and the soft energy absorbing layer provides a transition between the impact beam and the front fascia panel so as to allow the system to conform to the desired shape of the front fascia panel which may have significant angles and forms required by the vehicle styling. The hard energy absorbing layer and the soft energy absorbing layer also provide a transition between the fascia panel and the impact beam to effectively absorb low speed impacts without compromising system integrity.
It is known in the art to provide vehicle impact beams that are sandwich structures having a thermoplastic core. These prior art impact beams can generally be categorized into three designs, namely, hollow beams that are fully or partially reinforced with a polymer or metallic foam, single or dual-sided facesheets reinforced with a honeycomb-like cellular core, and formed composite impact beams. For hollow metallic or polymer matrix composite tube structures, which are fully or partially reinforced with a lightweight foam core, the material used for the core can be either a metallic or polymeric foam that is bonded, mechanically attached or interference fit into the tube structure. The purpose of the core is to carry shear loads in the sandwich structure and absorb energy in the event of a low or high speed impact, which is a distinction dependent on the density and composition of the foam. The use of honeycomb or honeycomb-like ordered cellular cores to provide reinforcement to one or two flat facesheets have an open-sided sandwich designs and have honeycomb, discrete-stiffened or wine-crate structures extending from the front face of the impact beam back towards the passenger compartment of the vehicle. If a second facesheet is not included between the core and the passenger compartment, then the core material must be relatively dense since it provides most of the flexural stiffness to the structure adjacent to the shear load transfer.
The manufacturing process of a vehicle typically includes first fabricating a vehicle structure, frame or chassis, sometimes referred to as a body-in-white (BIW), that includes a special configuration of structural metal beams, members, elements, etc. secured together, such as by bolts, welding, glue, etc., that provides the structural foundation to which the other vehicle components are mounted. Once the BIW structure is assembled, it is further processed through various fabrication steps, such as pretreatment (PT) steps including de-greasing, phosphate conversion coating, etc., electrophoretic painting (ELPO), primer, paint, etc. However, some of the structural elements in the BIW structure do not require these processes, but are put through these processes because they are part of the BIW structure, which reduces manufacturing costs. Some of these processes are high temperature processes, for example, ELPO drying is performed in an oven that runs at temperatures of 170°-200° C. Because the elements of the BIW structure are made of metal, theses temperatures do not cause any adverse affects to the structure.
In one known vehicle design, a front vehicle bumper assembly of the vehicle is mounted to ends of vehicle side rails as part of the BIW structure that is subjected to the high temperature manufacturing processes. In that design, the front bumper assembly is entirely made of metal making it able to withstand the high temperature processes. However, as discussed above, vehicle manufacturers are moving towards making various vehicle impact beams as sandwich structures having thermoplastic parts. Most thermoplastic materials will lose their structural integrity and melt at temperatures above, for example, 150° C., thus making them unusable as part of an impact beam for a BIW. Alternatives can be provided, including making the thermoplastic core out of a high cost thermoset material that can stand the high BIW processing temperatures. However, this adds significant and undesirable cost to the manufacturing process. Further, it is possible to provide a temporary beam member in place of the sandwich structure during the BIW fabrication process, which can later be removed during assembly and replaced with the sandwich structure. However, this process also adds undesirable cost to the manufacturing process.